# Comparative Analysis of PRV-1 in Atlantic Salmon and PRV-3 in Coho Salmon: Host-Specific Immune Responses and Apoptosis in Red Blood Cells

## TL;DR

This study compares how red blood cells from two types of salmon respond differently to two types of PRV, revealing insights into the virus's impact on fish health.

## Contribution

The study reveals species-specific immune and apoptotic responses of red blood cells to PRV-1 and PRV-3 in two salmon species.

## Key findings

- PRV-3 infection in coho salmon RBCs caused significant apoptosis and metabolic disruption from 7 dpi.
- Atlantic salmon RBCs showed limited apoptosis and a weaker antiviral response to PRV-1.
- Coho salmon RBCs exhibited morphological changes but no hemolysis following PRV-3 infection.

## Abstract

Fish red blood cells (RBCs) are nucleated, transcriptionally active, and key players in both gas transport and immune responses. They are the primary targets of Orthoreovirus piscis (PRV), the etiological agent of heart and skeletal muscle inflammation (HSMI), which includes three genotypes (PRV-1, PRV-2, and PRV-3), linked to circulatory disorders in farmed salmon. In Chile, PRV-3 affects the coho salmon (Oncorhynchus kisutch), but host–pathogen interactions remain poorly characterized. This study compared the interactions of PRV-3 in coho salmon and PRV-1 in Atlantic salmon (Salmo salar) using RBC infection models. RBCs were isolated from healthy juvenile salmon (n = 3) inoculated with either PRV-1 (Ct = 18.87) or PRV-3 (Ct = 21.86). Poly I:C (50 µg/mL) was used as a positive control for the antiviral response. Cells were monitored for up to 14 days post-infection (dpi). PRV-3 infection in coho salmon RBCs caused significant metabolic disruption, apoptosis from 7 dpi, and correlated with increasing viral loads. In contrast, PRV-1 infection in Atlantic salmon RBCs showed limited apoptosis and maintained cell viability. Coho salmon RBCs upregulated rig-i, mx, and pkr transcripts, indicating activation of the type I interferon pathway, whereas Atlantic salmon RBCs exhibited a more attenuated response. PRV-3 induced notable morphological changes in coho salmon RBCs, although neither PRV-3 nor PRV-1 caused hemolysis. These findings highlight species-specific differences in RBC responses to PRV infection and provide new insights into the pathogenesis of PRV-3 and PRV-1.